Water mammals such as dolphins, whales, mermaids, and manatee obtain their water through the food they eat. The fish or grasses contain high amounts of water in relation to the high salinity of their surroundings. This is how they remain hydrated. I am ready to pick up my Nobel Prize now.

they get all their moisture from thier food but they cannot tell the difference between being hungry and being thursty. in captivity dolphins will drink fresh water from a hose pipe but then they will not eat for a week.

Dolphins and whales obtain water from the fats in their food. Having worked with captive dolphins I can confirm they will drink from hose pipes but it is not true that they will then not eat for a week after doing this. In fact, an old veterinary tricks to stimulate fasting dolphins to eat was to place them in a fresh water environment for a short period of time.

So, this means that if a cetacean can't find food, it will die of thirst before dying of hunger? If it takes less time to die of thirst than hunger doesen't that make it alot more urgent for marine mammals to find food?

aquatic animals drink water; indeed it would be pretty difficult to keep from gulping it down while eating. Those in saltwater have to do something so they don't shrivel up and die as the water leaves their bodies to surround the salt outside. Osmoconformers adjust their bodies so they can deal with a high salinity in side. Osmoregulators excrete the salt in concentrated form, after having absorbed as much of the water as possible being excreting it. Some have special features like salt glands, and some just excrete it in their urine.

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Dolphins and whales do not drink. Just as we humans cannot use salt water as our source of water, neither can marine mammals. This is because they would need to ingest more fresh water than the seawater they consume in order to excrete the salt it contains.

Much of their water comes from fish and squid, which can contain more than 80 per cent water by mass. They can also obtain water through metabolising fat. In order to reduce their water loss they have similar internal designs to those of desert-dwelling mammals, including a long loop of Henle in the kidney nephron.

As well as internal adaptations, marine mammals did away with sweat glands to stop any water loss through sweating. Instead, they use their surroundings to cool down.

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Marine mammals certainly are less prone to thirst than land-dwelling mammals; for one thing, they have no need to sweat. They do not swallow any more salt water than they can help, though. Unlike seabirds and turtles, they lack special salt-excreting glands, so every bit of salt they swallow exacts a penalty.

However, whales eat animals, and sirenians (manatees and dugongs) eat plants. In such foods salt is as little as one-fifth as concentrated as in seawater because the prey has expended energy to excrete salt.

You might say that marine mammals rely on their food to desalinate their water. Even mammalian prey can contribute to this process as they eat low-salt organisms.

Interestingly, as they are unable to sweat or increase their water intake dramatically when thirsty, whales and seals are vulnerable to changes, especially increases, in water temperature. In particular, many species have great difficulty crossing the equator, while most are comfortable as close to the poles as foraging will take them.

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